He'd lobbied for underground trains throughout the 1840s, but opponents thought the idea was impractical since the railroads at the time only had short tunnels under hills.

他在 1840 年代间不停游说当局开建地下铁路。然而，他的反对者认为这个想法是不切实际的，因为当时铁路只有通过山丘时才有隧道。

The only one that did progress was this short tunnel in Las Vegas, which opened in 2021. You've done it again, Elon — classic gadgetbahn.

唯一取得进展的是拉斯维加斯的这条短隧道，它于 2021 年开放。埃隆，你又做到了——经典的 gadgetbahn。

After the steps there was a short tunnel, high enough for them to walk erect in, and then they reached the cave itself and paused in wonder and admiration.

台阶之后是一条短隧道，高到足以让他们直立行走，然后他们到达了洞穴本身并在惊奇和钦佩中停下来。